问题描述
我正在学习C,我需要阅读一个文本文件,但是我只能使用“ write,malloc,free,open,read,close”。
那是我的代码:
#define MAXCHAR 10000
int open_fp(int check)
{
char *int_vector;
int fp,len;
int i,j;
char buffer[MAXCHAR];
if(check == 0) //standard list
{
if((fp = open("file.txt",O_RDONLY)) != -1) //check if the fp is opened. -1 = error
{
printf("\n%d\n",fp); // DEBUG FUNCTION
sleep(1);
if (!(int_vector = (char*)malloc(sizeof(char) * sizeof(char))))
{
printf("\nWrong allocation\n!"); // DEBUG FUNCTION
return(0);
}
len = read(fp,int_vector,MAXCHAR);
for(i=0;i<len;i++)
{
printf("%c",int_vector[i]);
}
}
else
{
printf("File error!");
return (0);
}
}
return(0);
}
现在我的问题是:您可以在这里阅读
char buffer[MAXCHAR];
我已经创建了静态缓冲区,但是我想创建一个动态缓冲区,该缓冲区允许我根据文本文件中字符的数量来调整缓冲区的大小,但是我不知道如何...有人将???
解决方法
首先,您在下面一行中分配内存的方式是错误的。
//This allocates only 2 bytes of memory,but you are trying to read 10000
if (!(int_vector = (char*)malloc(sizeof(char) * sizeof(char))))
如下更正该行
//better to add one byte extra and store \0 at the end,useful in case of string operations
if (!(int_vector = malloc(MAXCHAR+1)))
就您的问题而言,在这种特殊情况下,您不需要重新分配内存,因为您只是读取要缓冲的字节并进行打印。
一个malloc
就足够了。
#include<stdlib.h>
#include<stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define MAXCHAR 100
int open_fp(int check)
{
char *int_vector;
int fp,len;
int i,j;
char buffer[MAXCHAR];
if(check == 0) //standard list
{
if((fp = open("file.txt",O_RDONLY)) != -1) //check if the fp is opened. -1 = error
{
printf("\n%d\n",fp); // DEBUG FUNCTION
sleep(1);
if (!(int_vector = (char*)malloc(MAXCHAR)))
{
printf("\nWrong allocation\n!"); // DEBUG FUNCTION
return(0);
}
//not doing memset on purpose because only limited bytes are accessed.
while(len = read(fp,int_vector,MAXCHAR))
{
printf("\n **number of bytes read is %d **\n",len);
for(i=0;i<len;i++)
{
printf("%c",int_vector[i]);
}
}
printf(" At last LEN = %d\n",len);
//free the memory at the end
free(int_vector);
int_vector = NULL;
close(fp);// better to as fd
}
else
{
printf("File error!\n");
return (0);
}
}
return(0);
}
int main()
{
open_fp(0);
return 0;
}
,
ehm,如果您也忘记设置realloc
,下面是一些用于重新分配(动态调整大小缓冲区)的示例代码
#include <stdio.h>
#include <stdlib.h>
int main () {
char *str;
/* Initial memory allocation */
str = (char *) malloc(15);
strcpy(str,"tutorialspoint");
printf("String = %s,Address = %u\n",str,str);
/* Reallocating memory */
str = (char *) realloc(str,25);
strcat(str,".com");
printf("String = %s,str);
free(str);
return(0);
}